Attribution modeling is the process of attributing value and/or conversions to the marketing events which may have influenced a user prior to converting. Conversions may be defined as any action an content provider (e.g., advertiser) desires a user to take. Attribution modeling uses observations of user-level marketing events and interactions with the content provider as input to approximate causal impact of specific content items. One problem in the field of attribution modeling is selecting activity stream data that will generate accurate estimations of a content item's (e.g., advertisement's) causal impact. Generally, content impressions and user interactions with the content provider (e.g., advertiser) are tracked by a system which includes logging user identifications in lists and maintenance of these lists.